1. Field of the Invention
The present invention relates to a designing method of leadframe tip arrangement and, more specifically, to a designing method for arranging leadframe tips at a constant lead pitch.
2. Background Art
First, an example of a conventional designing method of leadframe tip arrangement will be described.
FIGS. 5 and 6 show a conventional designing method of leadframe tip arrangement. More specifically, FIG. 5 shows a 1/4 model of a leadframe tip arrangement diagram and FIG. 6 shows a definition of lead pitches.
In FIGS. 5 and 6, reference numeral 1 denotes a die pad outline, numeral 2 denotes a chip outline, numeral 3 denotes a reference point, numeral 4 denotes a leadframe tip arrangement line, numeral 5 denotes an end point of the leadframe tip arrangement line 4, numeral 6 denotes the other end point of the leadframe tip arrangement line 4, and numerals 7-16 denote leadframe tip portions.
In FIG. 6, reference numerals 19 and 20 denote leadframe tip pitches (i.e., lead pitches), and numeral 23 denotes a leadframe tip width (i.e., lead width). Reference numeral 25 denotes the central axis of a leadframe tip portion 7, and numeral 26 denotes an angle formed by the leadframe tip arrangement line 4 and the central axis 25. Further, in FIG. 5, reference numeral 30 denotes a die pad corner portion.
In this conventional method, the lead pitches 19 and 20 (see FIG. 6) are defined so as to equally divide the segment between the end points 5 and 6 of the leadframe tip arrangement line 4 (see FIG. 5). This causes a problem that the angle 26 (see FIG. 6) decreases and the lead width 23 becomes smaller as the leadframe tip portion comes closer to the die pad corner portion 30.
As described above, in the conventional designing method of leadframe tip arrangement, a leadframe tip arrangement line is equally divided and each divisional length is defined as a lead pitch. This results in the problems that leadframe tip portions in a die pad corner portion have smaller widths than those in a die pad central portion and that lead pitches and lead widths become not uniform. Further, the fact that lead widths become small may be disadvantageous to wire bonding due to limitations of the wire bonder.